Recently, as a quantity of data transmitted through a network increases according to necessity of mass information exchange, a wavelength division multiplexing (WDM) method has been used in an optical transmission system using a single channel. The WDM method is a data transceiving method of transceiving data of several wavelength ranges through one optical fiber by multiplexing or demultiplexing the data.
Accordingly, a multi-channel transmitter optical sub assembly (TOSA), a multi-channel receiver optical sub assembly (ROSA), and an optical sub assembly (OSA) are demanded as a multi-channel optical transceiver module for data channel multiplexing in an optical transceiver system to which a multi-function high-integrated optical transmission line optical sub module platform for a network based on a WDM is applied.
Especially, in a metro access network system requiring mass data transmission, the development of a technology of the multi-channel ROSA that is an optical receiver with high sensitivity has been demanded according to a long transmission distance. In order to manufacture the ROSA having high sensitivity, it is necessary to use a photodiode (hereinafter, referred to as a “PD”) having a high sensitivity characteristic. However, it is more difficult to manufacture the ROSA having high sensitivity in which the PDs are integrated, compared to the ROSA in which PIN PDs are integrated in the related art.
FIGS. 1A and 1B are a diagram illustrating a configuration of a ROSA in which a single-channel PD is integrated in the related art and a circuit diagram corresponding to the configuration, respectively.
Referring to FIGS. 1A and 1B, the ROSA in the related art includes a PD 110, two bypass capacitors 120 and a transimpedance amplifier (TIA) 130.
In order to manufacture the ROSA having the best sensitivity, the PD needs to exhibit high sensitivity, and the sensitivity of the PD may be measured and evaluated when the ROSA is manufactured in a form of a transistor outline (TO) in which the two bypass capacitors 120 and the transimpedance amplifier 130 are integrated as illustrated in FIG. 1. Accordingly, the sensitivity of the ROSA in which the PD is integrated may be determined by an optimal arrangement of the PD 110, the two bypass capacitors 120 and the transimpedance amplifier 130, and a wire bonding method.
The transimpedance amplifier mounted for the optimal arrangement of the respective components of the ROSA needs to meet a capacitance of the PD demanded for an optimum operation, and also meet a capacitance of the bypass capacitor. Further, when a length of the wire for the wire bonding increases, inductance increases, so that it is necessary to arrange the respective components considering the inductance so as to optimally perform the wire bonding.
As described above, in order to manufacture the ROSA, it is necessary to consider several factors. In order to meet the consideration, sizes of the three types of components, such as the PD, the two bypass capacitors and the transimpedance amplifier, the arrangement for the mounting and an electrode design are important. In the three types of components, a size of the currently commercially available transimpedance amplifier and a size of the capacitor of optimal capacity are larger two and three times than that of the PD. However, when a size of the PD increases, the capacitance of the PD increases and a chip price is increased, so that it is impossible to increase a chip size of the PD to correspond to the sizes of the transimpendance amplifier and the capacitor in order to achieve the optimal wire bonding for preventing the deterioration of the sensitivity. Accordingly, a shape of the ROSA to be manufactured is determined according to the sizes of the transimpendance amplifier and the capacitor and an arrangement form of electrode pads of the PD.
Further, in order to manufacture the ROSA in which a plurality of PDs is integrated, since there is no commercially available multi-channel transimpedance amplifier, it is necessary to integrate the transimpedance amplifiers and the capacitors as many as the number of channels. Accordingly, it is difficult to manufacture the ROSA in which the plurality of PDs having a high sensitivity characteristic is integrated, and a sub module platform in which the ROSA in which single-channel PDs are integrated as many as the number of channels has been developed up to now.